A conventional article of athletic footwear includes two primary elements, an upper and a sole structure. The upper is often formed of leather, synthetic materials, or a combination thereof and comfortably secures the footwear to the foot, while providing ventilation and protection from the elements. The sole structure generally incorporates multiple layers that are conventionally referred to as an insole, a midsole, and an outsole. The insole is a thin cushioning member located within the upper and adjacent the sole of the foot to enhance footwear comfort. The midsole, which is traditionally attached along its peripheral edge to the upper, forms the middle layer of the sole structure and serves a variety of purposes that include controlling potentially harmful foot motions such as pronation, attenuating ground reaction forces, and absorbing energy. In order to achieve these purposes, the midsole may have a variety of configurations. The outsole forms the ground-contacting element of footwear and is usually fashioned from a durable, wear resistant material that includes texturing to improve traction.
The primary element of a conventional midsole is a resilient, polymer foam material that extends throughout the length of the footwear. The properties of the polymer foam material can be varied to regulate the relative stiffness, degree of ground reaction force attenuation, and energy absorption properties of the midsole to accommodate the specific demands of the activity for which the footwear is intended to be used.
Conventional midsoles may also include, for example, stabilizing devices that resist over-pronation and moderators that distribute ground reaction forces. Stability devices are often incorporated into the polymer foam material of the midsoles to control the degree of pronation in the foot. Examples of stability devices are found in U.S. Pat. No. 4,255,877 to Bowerman; U.S. Pat. No. 4,287,675 to Norton et al.; U.S. Pat. No. 4,288,929 to Norton et al.; U.S. Pat. No. 4,354,318 to Frederick et al.; U.S. Pat. No. 4,364,188 to Turner et al.; U.S. Pat. No. 4,364,189 to Bates; and U.S. Pat. No. 5,247,742 to Kilgore et al. In addition to stability devices, conventional midsoles may include fluid-filled bladders, as disclosed in U.S. Pat. Nos. 4,183,156 and 4,219,945 to Marion F. Rudy, for example.
To provide increased sidewall stabilizing support, known footwear simply provides additional materials and/or structures to the sidewalls, thereby increasing the complexity of the manufacture of the footwear and its cost. U.S. Pat. No. 5,896,683 to Foxen et al. provides a plurality of finger-like elements that extend from the sole vertically along the upper.
It is an object of the present invention to provide a variable support structure for an article of footwear that reduces or overcomes some or all of the difficulties inherent in prior known devices. Particular objects and advantages of the invention will be apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this field of technology, in view of the following disclosure of the invention and detailed description of certain preferred embodiments.